Several species of mammalian C-type viruses contain structural proteins which share antigenic determinants with proteins from other species of RNA tumor viruses. The viral polypeptides which contain these common determinants are available in highly purified and immunologically active forms. Antibodies have been raised against these viral interspecies components and used as probes for the screening of human carcinomas for similar viral proteins. Studies have provided immunological and biochemical evidence that an oncogenic viral genome may reside within human tumor cells both in vivo and after culture in vitro. Human malignant and benign prostate tissue will be obtained from surgery and will be established in monolayer tissue culture. Extracts prepared from these prostatic tissues will be examined by competition radioimmunoassay for the demonstration of any immunologic activity with antiserum prepared against antigenic determinants common to RNA tumor viruses. Extracts demonstrating viral antigenic activity will be extensively analyzed in a two-phase, two-dimensional immunoelectrophoresis system to size and isolate the reacting proteins. Patient sera will be collected and analyzed for immunological responses to prostatic tissue extracts in radioimmunoassays and for screening of reactions with isolated interspecies viral antigens. Cytotoxic activities of patients sera against prostate cells in vitro and against prostate cells passaged through nude mice will also be determined. Cytogenetic patterns of the original surgical tissues and of the tissue-cultured cells will be studied to determine the extent of numerical and structural chromosome abnormalities in attempts to specify chromosome patterns. Cytological data will be correlated with the morphological and physiological traits of the cells and with the relationship between specific chromosome abnormalities and the presence of viral proteins. Localization of viral-like proteins within prostate cells will be determined by peroxidase and ferritin labeling procedures followed by visualization in electron microscopy.